Image forming apparatus with variable capacity cleaning means

ABSTRACT

An image forming apparatus includes: an image carrying member for carrying an image; a recording material carrying member for carrying a recording material; a transfer device for transferring the image from the image carrying member to the recording material carried by the recording material carrying member; and a cleaning device for cleaning the recording material carrying member, wherein, when images are formed successively on a plurality of recording materials, the cleaning capacity of this cleaning device is made larger as a distance between the rear end of a recording material and the forward end of the next recording material becomes larger.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic image formingapparatus, such as a copying apparatus, a laser beam printer or afacsimile apparatus and, in particular, to a cleaning means to be usedin such an image forming apparatus.

2. Description of the Related Art

Conventionally, there have been proposed various image formingapparatuses which are equipped with a plurality of image formingsections and in which toner images of different colors are formed in theimage forming sections, the toner images being sequentially superimposedone upon the other on the same recording material to thereby provide acolor image.

In such a color image forming apparatus, foreign matter such as toner,lubricant oil or dust is usually allowed to adhere to the image carrierfor carrying toner images formed thereon, the recording materialcarrying member for carrying the recording material and guiding it tothe transfer section where image transfer from the image carrier iseffected, etc. Such foreign matter, which may contaminate the recordingmaterial, must be removed by cleaning.

When the image forming speed of the image forming apparatus isrelatively high, or when the amount of lubricant oil is increased as aresult, for example, of using a sharp melt type toner, which isdescribed below, a higher level of cleaning performance is required.

An electrophotographic multi-color copying machine of the type whichuses an endless recording material carrying member is in use forhigh-speed recording.

In such an image forming apparatus, the recording material, which iscarried by a feeding belt constituting the recording material carryingmember, is conveyed to the transfer position of each of a plurality ofimage carriers (photosensitive drums). Then, cyan, magenta, yellow andblack toner images are transferred one by one from the respective imagecarriers to the recording material carried by the feeding belt. Afterthe image transfer has been completed, the recording material isconveyed to a fuser, where the toners of these colors are melted andmixed with each other, whereby a full-color toner image is fixed to therecording material. The fuser is equipped with a fixing roller which isheld in contact with the unfixed toner image on the recording material,and a pressurizing roller which is in contact with the other side of therecording material. A lubricant such as silicone oil is applied to thefixing roller in order to prevent toner from adhering thereto.

After the completion of image transfer, the portion of toner remainingon the feeding belt and any foreign matter thereon are removed bycleaning by using a cleaning member which is brought into contact withthe surface of the feeding belt.

However, the above construction has a problem in that the portion of thefeeding belt where there is no recording material is subject tocontamination with toner during the image transfer process. For example,some of the toner on the photosensitive drum may be scattered on thisportion due to pretransfer discharge, which occurs immediately beforethe transfer position, or some of the unfixed toner transferred to therecording material may be scattered on this portion of the belt at thetime of separation from the photosensitive drum. Further, fog toner onthe photosensitive drum may be transferred to the belt, or toner may beallowed to drop directly onto it from the developing device or thecleaner for the photosensitive drum.

A cleaning member for removing toner adhering to the conveying belt, forexample, a cleaning web (made of a nonwoven fabric) is attached to thesurface of the conveying belt. As compared with the case in whichcopying is performed on a single sheet, the case in which copying issuccessively performed on a plurality of sheets has a problem in that alarge amount of toner is allowed to remain on the belt in a short time.The amount of toner remaining on the belt depends upon the number ofsheets on which copying is performed. Thus, in the latter case, animprovement in cleaning performance is required.

Further, in high-speed apparatuses, full-color apparatuses or the like,when the high voltage for image transfer is applied to the transfercharger even during inter-sheets periods (time intervals between sheetsin the case of successive copying) in order to simplify the controlsequence, the fog toner on the photosensitive drum is easily allowed tobe transferred.

Further, to maintain satisfactory fixing conditions, when the thicknessof the recording material is large, the fixing speed is decreased ascompared to the usual case and, at the same time, the intervals betweensheets in successive copying is enlarged. Further, due to the differencein size of the recording material, for example, the difference in sizebetween an A4 size paper and a post card, a difference is generated interms of the toner contamination of the feeding belt (as a result ofscattering of unfixed toner images on the recording material) in thethrust direction thereof (the direction which is perpendicular to thedirection in which the belt runs).

Further, in a both-side type machine which is capable of forming imageson both sides of a recording material, the oil adhering to the recordingmaterial during the fixing on the first surface of the recordingmaterial is allowed to be transferred to the feeding belt during theimage transfer on the second surface of the recording material. Sincethe oil easily comes into close contact with the remaining toner on thefeeding belt, it is difficult to remove the oil and toner by cleaning.According to a measure for preventing this oil from being transferred tothe photosensitive drum, the photosensitive drum is constantly coatedwith toner, which toner functions as a spacer between the photosensitivedrum and the feeding belt. However, this results in the amount of tonertransferred to the feeding belt being increased accordingly.

When the next recording material is attracted to the feeding beltwithout having clearing away such residual toner contamination on thefeeding belt, the residual toner is transferred to the back side of therecording material and fixed thereto. Accordingly, a backside of thecopy image whose back side becomes contaminated. This problem has notbeen solved yet. In an apparatus having a both-side copying function,image formation is also performed on the back side of the recordingmaterial, which is contaminated with the residual toner, with the resultthat the images formed on the first and second sides are both defectiveimages contaminated with residual toner.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image formingapparatus which is capable of satisfactorily clearing away contaminationof the recording material carrying member due to scattered toner, fogtoner, etc. regardless of the degree of contamination.

Further objects and features of the present invention will become moreapparent from the following detailed description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the construction of a feeding beltcleaning unit;

FIG. 2 is a schematic diagram showing the construction of a recordingmaterial thickness detecting sensor;

FIG. 3 is a schematic diagram showing the construction of an example ofan image forming apparatus; and

FIG. 4 is a schematic diagram showing the construction of anotherexample of a feeding belt cleaning unit.

FIG. 5 is a schematic diagram showing the construction of yet anotherexample of a feeding belt cleaning unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the image forming apparatus of the present invention willnow be described with reference to the drawings.

As an image forming apparatus, an example of a color electrophotographicrecording apparatus will be described with reference to FIG. 3. In theapparatus, a first, a second, a third and a fourth image formingsections Pa, Pb, Pc and Pd are arranged side by side. In these imageforming sections, toner images of different colors are formed by thesteps of latent image formation, development and transfer.

The first through fourth image forming sections Pa through Pd areequipped with dedicated image carrying members, which, in this example,are electrophotographic photosensitive drums 3a, 3b, 3c and 3d. Thetoner images of different colors are formed on the photosensitive drums3a through 3d. A recording material carrying member 130 (feeding belt)is provided adjacent to the photosensitive drums 3a through 3d, and thetoner images of different colors formed on the photosensitive drums 3athrough 3d are transferred to a recording material P carried and fed bythe feeding belt 130. Further, the recording material P, to which thetoner images of different colors have been transferred, undergoes thefixing of the toner images in a fixing section 9 by heating andpressurizing. After this, the image is discharged out of the apparatusas the recording image.

In the periphery of the photosensitive drums 3a through 3d, there areprovided exposure lamps 111a, 111b, 111c and 111d, drum chargers 2a, 2b,2c and 2d, electric potential sensors 113a, 113b, 113c and 113d,developing devices 1a, 1b, 1c and 1d, brush-type transfer chargers 24a,24b, 24c and 24d, and cleaners 4a, 4b, 4c and 4d, respectively. Further,in the upper section of the apparatus, a light source device (not shown)and a polygon mirror 117 are provided.

Scanning is performed with a laser beam emitted from the light sourcedevice by rotating the polygon mirror 117. The scanning beam isdeflected by a reflection mirror, and condensed on the generatrix of thephotosensitive drums 3a through 3d for exposure, thereby forming latentimages in accordance with an image signal on the photosensitive drums 3athrough 3d.

The developing devices 1a through 1d are filled with a predeterminedamount of toners of cyan, magenta, yellow and black, respectively, whichare supplied as the developer by supplying devices (not shown). Thedeveloping devices 1a through 1d develop the latent images on thephotosensitive drums 3a through 3d to visualize the cyan toner image,the magenta toner image, the yellow toner image and the black tonerimage.

The recording materials P are accommodated in a recording materialcassette 10, from which they are supplied to the feeding belt 130 by wayof a plurality of feeding rollers and resist rollers 12, and aresuccessively supplied to transfer sections opposed to the photosensitivedrums 3a through 3d by being fed by the feeding belt 130.

The feeding belt 130 consists of a dielectric resin sheet such as apolyethylene terephthalate resin sheet (PET sheet), a polyvinylidenefluoride resin sheet, or a polyurethane resin sheet. The ends of thebelt are superimposed one upon the other and joined to each other toform an endless belt. Alternatively, a belt having no seam (seamlessbelt) may be used.

When this feeding belt 130 rotates until it is made sure that it is at apredetermined position, the recording material P is fed to the feedingbelt 130 from the resist rollers 12, and the recording material P is fedto the transfer section of the first image forming section Pa. At thesame time, an image writing signal is turned ON, and using this as areference, image formation is performed on the photosensitive drum 3a ofthe first image forming section Pa with a predetermined timing. In thetransfer section underneath the photosensitive drum 3a, the brushtransfer charger 24a imparts an electric field or a charge, whereby thetoner image of the first color formed on the photosensitive drum 3a istransferred to the recording material P. By this transfer process, therecording material P is firmly held by the feeding belt 130 byelectrostatic attraction, and fed to the second image forming sectionPb, etc.

Image formation and transfer are similarly conducted in the secondthrough fourth image forming sections Pb through Pd. Then, the recordingmaterial P, to which the toner images of four colors have beentransferred, undergoes charge removal by a separation charger 32 on thedownstream side with respect to the feeding direction of the feedingbelt 130 to thereby attenuate the electrostatic attracting force,whereby it is separated from the end portion of the feeding belt 130.The separated recording material P is conveyed to the fuser 9 by aconveying section 62.

The fixing device 9 comprises a fixing roller 51, a pressurizing roller52, heat-resistant cleaning members 54 and 55 for cleaning each of them,roller heating heaters 56 and 57 installed in the rollers 51 and 52, anapplication roller 50 for applying lubricant oil such as dimethylsilicone oil to the fixing roller 51, an oil sump 53 for the oil, and athermistor 58 for detecting the surface temperature of the pressurizingroller 52 to control the fixing temperature.

By the fixing operation, the toner images of four colors transferred tothe recording material P are mixed together and fixed to the recordingmaterial P to thereby form a full-color copy image.

The color toners are required to exhibit a satisfactory melting propertyand mixing property when heated in the fixing device 9. When theirmelting property and mixing property are insufficient, the amount of airgaps between toner particles increases, with the result that the propertones of the pigments are impaired through the scattering light at theinterface between the toner and the air. Further, where toners aresuperimposed one upon the other, the lower toner is covered up by theupper toner, resulting in a deterioration in color reproducibility. As atoner satisfying such requirement in terms of melting property andmixing property, a so-called sharp melt type toner, which has a lowsoftening point and a low melting viscosity is used. By using such asharp melt type toner, an improvement is achieved in terms of colorreproducibility, thereby making it possible to obtain a color copyfaithful to the original.

However, the sharp melt type toner has a problem in that it has a greataffinity, so that it easily causes offset to the roller 51 of the fixingdevice 9. In the fixing device, pressurization is effected in additionto heating. A toner which has a great affinity is liable to betransferred and adhere to the fixing roller as a result of thepressurization and the heating. This toner will adhere to the nextrecording material or set on the fixing roller, resulting in andefective image.

A lubricant oil such as dimethyl silicone is used for the purpose ofpreventing the generation of such a defective image. Prior to the fixingof the toner image to the recording material, the lubricant oil isapplied to the fixing roller. Due to this arrangement, when therecording material to which the toner image has been transferredundergoes heating and pressurization, the fixing roller is brought intocontact with the toner image through the intermediation of the lubricantoil, which means there is no direct contact between them, therebyeffectively preventing toner from adhering to the fixing roller.

When the image transfer has been completed, the toner remaining on thephotosensitive drums 3a through 3d is removed by the cleaning blades ofthe respective cleaners 4a through 4d, and the photosensitive drums aremade ready for the next latent image formation process, etc. The tonerportion remaining on the feeding belt 130 and any foreign matter thereonare wiped off by bringing the cleaning web 19 (non-woven fabric) intocontact with the surface of the feeding belt 130.

A pair of rollers 17 and 18 are provided below the downstream end of thefeeding belt 130. The cleaning web 19 is wound around one of theserollers, the web roller 18, from which it is fed, and is taken up by theother roller 17. Between the rollers 17 and 18, there is provided apressurizing roller 22, by means of which the cleaning web 19 is pressedagainst the surface of the feeding belt 130. The pressing of thecleaning web 19 against the feeding belt 130 by the pressurizing roller22 is backed up by an opposite roller 21 arranged on the back (inner)side of the feeding belt 130.

As preferable fibers for the cleaning web 19, it is possible to usefibers such as polypropylene, rayon, acryl, nylon, polyester, or vinylonor a fiber consisting of a mixture of these fibers.

In this image forming apparatus, it is possible to switch between aone-side copy mode in which image formation is effected only on one sideof the recording material and a both-side copy mode in which imageformation is effected on both sides of the recording material. When theboth-side copy mode is selected by the user, and both-side imageformation is to be effected on the recording material P, the recordingmaterial P is not conveyed to a paper discharge tray 63 after thetransfer to one side has been completed and the recording material haspassed the fixing device 9 but is conveyed to a feeding path 65 to beexclusively used for both-side image formation by a flapper (reversingmember) 64 or the like. Then, the recording material P is reversedupside down and the feeding belt 130 is run again to perform imageformation again on the surface (second surface) of that side of therecording material which is opposite to the surface (first surface) ofthe side on which image formation has been completed. At this time,there is a fear the lubricant oil adhering to the first side of therecording material P and, in particular, to the toner image thereon,will adhere to the surface of the feeding belt 130. Further, there is afear that the oil from the feeding belt 130 transferred to thephotosensitive drums 3a through 3d will adhere thereto and contaminatephotosensitive drums 3a through 3d.

Since the cleaning blades of the cleaners 4a through 4d for thephotosensitive drums 3a through 3d are mainly provided for the purposeof removing toner on these photosensitive drums, it is difficult tosufficiently remove the lubricant oil adhering thereto. As a result,there arises the problem of a defective image due to lubricant oilcontamination of the photosensitive drums, which is a problem peculiarto both-side color copying (image formation). In view of this, thecleaning web 19, which is a cleaning member for cleaning the feedingbelt 130, removes not only the residual toner on the surface of thefeeding belt 130 but also the lubricant oil adhering to the surface.

FIRST EMBODIMENT

A first embodiment of the present invention will be described withreference to FIG. 1, which is an enlarged view of a part of theapparatus shown in FIG. 3. The components which are the same as thosedescribed above will be indicated by the same reference numerals andcharacters.

The cleaning unit C serving as the cleaning means for the feeding beltshown in FIG. 1 is arranged below the fourth image forming section Pdwhich is at the downstream side end with respect to the recordingmaterial conveying direction and below the portion where the movementtoward the upstream side with respect to the recording materialconveying direction is started. It is equipped with a web roller 18 fora cleaning web serving as the cleaning member, a take-up roller 17, andpressurizing rollers 21 and 22 which are arranged between the rollers 18and 17 and which press the cleaning web 19 against the lower surface ofthe feeding belt 130.

In the above-described construction, the remaining toner on that surfaceof the feeding belt 130, moving upstream with respect to the recordingmaterial feeding direction, which is in contact with the photosensitivedrums 3a through 3d is wiped off by the cleaning web 19, the cleaningweb 19 and the feeding belt 130 being held between and pressurized bythe pressurizing rollers 21 and 22.

In this embodiment, the feeding belt 130, which is an endless recordingmaterial carrying member, has a thickness of 150 μm, a width of 330 mmin the thrust direction perpendicular to the rotating direction, and acircumferential length of 1330 mm, and is rotated at a speed of 100mm/sec. The feeding of the recording material P by the feeding belt 130is effected in the direction of the fourth image forming section Pd fromthe first image forming section Pa.

That surface of the cleaning web, serving to remove the remaining toneron the feeding belt, which is in contact with the feeding belt has theabove-mentioned remaining toner embedded between the cleaning webfibers, so that the take-up roller 17 is rotated by a motor (not shown)to take up the cleaning web 19 to thereby cause a different portion ofthe surface of the cleaning web 19 to come into contact with the feedingbelt 130. That is, the cleaning web surface portion in contact with thefeeding belt 130 is changed.

In an example, this change may be effected by taking up the cleaning webby a predetermined amount for a predetermined period or for apredetermined number of sheets on which copying is effected. Forexample, assuming that the amount taken up at one time is approximately5 mm, as measured from the contact nip where the cleaning web 19 is heldbetween the pressurizing rollers 21 and 22 and in contact with thefeeding belt 130, the cleaning web is taken up for each 15-minuterotation of the feeding belt.

In the above control method, the feeding belt is satisfactorily cleanedin the case of a single sheet copying. However, when a plurality of A4size sheets are successively copied, the amount of toner scattered onthe feeding belt is much larger. For successive operations, the amountof scattered toner is several times the amount, as compared to the caseof a single sheet copying, that is scattered over or transferred to thefeeding belt. Accordingly, the scattered toner and fog toner remainingon the feeding sheet if not wiped off by the cleaning web is accumulatedon the feeding belt in a short time. Thus, the back side of the nextsheet for copying is contaminated with the remaining toner.

In view of this problem, in this embodiment, the setting in which thecleaning web is taken up by approximately 5 mm for each 15-minuterotation of the feeding belt is not adopted. Instead, in the case ofsuccessive copying on a plurality of recording materials, in the timingwith which the cleaning web is reduced. This will be described below indetail.

As shown in FIG. 1, a separation guide 66 is provided for guiding therecording material separated from the feeding belt 130. This separationguide 66 is equipped with a separation jam sensor 66a for checkingwhether the separation of the recording material has been effected ornot. This separation jam sensor 66a detects the period of time from theinstant a recording material has passed it to the instant the passing ofthe next recording material starts. The detection result is supplied toa control unit (not shown) to be electrically processed as data. On thebasis of such data, the motor of the take-up roller 17 is controlled bya processing device.

Table 1 shows inter-sheet distance, i.e. the distance the rear end of arecording material and the forward end of the next recording material onthe conveying belt and the detection times of the above separation jamsensor in the case of successive copying by the apparatus of thisembodiment for different recording material sizes. The successivecopying is a mode of copying in which images are successively formed ona plurality of recording materials in response to a single imageformation signal input from outside. In successive copying, a pluralityof recording materials are simultaneously carried by the feeding belt.

                  TABLE 1                                                         ______________________________________                                                      Measured amount                                                                           Inter-sheet distance                                Size          (g/m.sup.2) detection time (sec.)                               ______________________________________                                        A4            80          0.30                                                A4            200         7.90                                                A4R (lengthwise feed)                                                                       80          0.38                                                A3            80          0.80                                                A4 (OHP)                  7.90                                                A4 (second side)                                                                            80          0.75                                                ______________________________________                                    

As shown in Table 1, when an A4 size thick paper sheet (200 g/m²) or anOHP transparent resin film is used, the inter-sheet distance isrelatively large as compared to the lateral feed (a manner of feeding inwhich the shorter side of an A4 size sheet is matched with the feedingdirection) of an ordinarily A4 size sheet (80 g/m²) in order to lowerthe fixing speed. Further, the inter-sheet distance is made relativelylarge in the second side of A4 size in order that the fixing speed islower in the fixing of the second side of the A4 size recording materialthan in that of the first side of the A4 size.

The necessity of switching the cleaning capacity in accordance with theinter-sheet distance, which is the problem to be overcome by the presentinvention, is shown in Table 1. To effect a satisfactory fixing of therecording material, the requisite heat amount is obtained by changingthe fixing speed, so that setting is effected such that the timing withwhich the recording material is fed (inter-sheet distance time) varies.Accordingly, the inter-sheet distance varies, and the amount of tonerscattered on the feeding belt and the amount of fog toner vary with theinter-sheet distance.

Table 1 shows only some types of recording materials. In order that theapparatus may be used for all types of recording materials, theinter-sheet distance detection times detected by the above-mentionedseparation jam sensor are classified in the processing device into fiveranks as shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                Inter-sheet distance                                                  Rank    detection time (sec.)                                                                      Control    Output timing                                 ______________________________________                                        Ref     (single sheet)                                                                             Ref        per 15 min.                                   A         0 ˜ 0.5                                                                            Ref × 0.9                                                                          per 13.5 min.                                 B       0.5 ˜ 1.5                                                                            Ref × 0.8                                                                          per 12 min.                                   C       1.5 ˜ 5.0                                                                            Ref × 0.7                                                                          per 10.5 min.                                 D       5.0˜   Ref × 0.6                                                                          per 9 min.                                    ______________________________________                                    

In Table 2, the case in which a single recording material is used forcopying is used as the reference rank. Ranks A through D are cases inwhich successive copying is performed on a plurality of recordingmaterials. Ranks differ according to the inter-sheet distance. Settingis made such that the larger the inter-sheet distance, the shorter thetake-up timing for the cleaning web.

In the control shown in Table 2, the A4 size recording material of 80g/m² shown in Table 1 is controlled in rank A, and the A4 size OHP filmis controlled in rank D. In these cases, the cleaning web is taken up byapproximately 5 mm per 13.5 minutes and 9 minutes, respectively. In thisway, the contaminated surface portion is replaced by a clean surfaceportion.

Thus, it is not only always possible to clean the feeding belt in asatisfactory manner but also to effect control according to the expectedamount of scattered toner and fog toner on the feeding belt, so thatthere is no need to forcibly change the surface portion of the cleaningweb when it still has a sufficient cleaning capacity, thereby achievinga substantial improvement in terms of the service life of the web.

In recent image forming apparatuses in which high quality images arerequired, there is provided a mode in which the user can manually selectthe degree of glossiness of the image. In this mode, control is effectedto change the fixing level of the un-fixed toner on the recordingmaterial by changing the fixing speed to thereby impart a variation inglossiness to the image. Thus, in this mode, the paper feed timing(inter-sheet distance) is different from that of the normal mode. Inthis way, it is effective as shown, for example, in Table 2, to vary theoutput timing for the cleaning web according to the glossiness modeselection.

SECOND EMBODIMENT

Next, a second embodiment of the present invention will be described.This embodiment is characterized in that the cleaning output iscontrolled in accordance not only with the inter-sheet distance but alsowith the recording material size.

This embodiment differs from the first embodiment in that theinter-sheet distance is fixed in A4 size ordinary paper (80 g/m²) and A3size ordinary paper (80 g/m²). That is, even when the ranks shown in thefirst embodiment are the same, if the recording material size differs,there may be a great difference in the total of inter-sheet distancespassing in a fixed period of time (for example, a period correspondingto one lap of the feeding belt), resulting in a difference in the amountof toner and fog toner on the feeding belt.

In the separation jam sensor of this embodiment, the total of periods inwhich the recording material passes in, for example, a minute, isdetected, and the detected time is supplied to a processing device (notshown) to be electrically processed. On the basis of the data thusobtained, the motor of the take-up roller 17 is controlled by theprocessing device.

Table 3 shows how the control is effected. In this embodiment, theoutput timing for the cleaning web in the case of an A4 size ordinarypaper (rank B) is shorter than that in the case of an A3 size ordinarypaper (rank A). Further, as in the first embodiment, since theinter-sheet distance is larger in the case of an A4 size thick sheet(200 g/m²) (rank D) or an A4 size OHP film (rank D) than in the case ofan A4 size ordinary paper, a reduction is accordingly achieved in termsof cleaning web output timing.

                  TABLE 3                                                         ______________________________________                                                Recording material                                                    Rank    pass detection time                                                                        Control    Output timing                                 ______________________________________                                        Ref     (single sheet)                                                                             Ref        per 15 min.                                   A           50 ˜ (Sec)                                                                       Ref × 0.9                                                                          per 13.5 min.                                 B       40 ˜ 50                                                                              Ref × 0.8                                                                          per 12 min.                                   C       30 ˜ 40                                                                              Ref × 0.7                                                                          per 10.5 min.                                 D        ˜30   Ref × 0.6                                                                          per 9 min.                                    ______________________________________                                    

According to Table 2, a sum total of the inter-sheet distances passingin a fixed period of time, i.e., the smaller the recording materialdetection time becomes larger passing in a fixed period of time, theoutput timing for the cleaning web 19 becomes shorter, thereby enhancingthe cleaning capacity.

The cleaning capacity can be switched according to the sum total of theinter-sheet distances passing in a fixed period time, whereby it isalways possible to clean the feeding belt as satisfactorily as or betterthan in the first embodiment.

THIRD EMBODIMENT

Next, a third embodiment of the present invention will be described withreference to FIG. 2. This embodiment is characterized in that thecleaning capacity of the cleaning web 19 is switched according to thesize of the recording material with respect to the directionperpendicular to the feeding direction and the thickness thereof.

While the first and second embodiments have been described mainly fromthe viewpoint of the inter-sheet distance, the width of the recordingmaterial in the direction perpendicular to the direction in which thefeeding belt runs is as important a parameter as the inter-sheetdistance in determining the contamination of the feeding belt withscattered toner.

That is, if the inter-sheet distance is the same, there is a greatdifference between A4 sheet and A6 size post card in terms of the areaof the exposed surface portion of the feeding belt during which therecording material is being attracted.

Thus, in this embodiment, recording material size data from cassettedetection and recording material size data obtained through manualsetting by the user are supplied to a processing device and, on thebasis of the data thus obtained, the motor of the take-up roller for thecleaning web is controlled. As a result, a satisfactory cleaning isrealized with a simple construction.

Apart from the recording material size, data on the thickness of therecording material may be used. For example, a sensor 100 for detectingthe thickness of the recording material as shown in FIG. 2 may beprovided, and data thereby obtained may be processed together with thedata on the recording material size, whereby it is possible to performcleaning in a more satisfactory manner.

With reference to FIG. 2, the manner in which the thickness of therecording material is detected by the sensor will be described.

When the forward end of the recording material 20, conveyed from theupstream side, reaches the transmission type photo sensor 100, lightapplied to the sensor 100 is intercepted and the output of the sensor100 changes, whereby the reaching of the recording material is detected.At the same time, a CPU 101 drives a drive source 102, whereby a pair orrollers consisting of a feeding roller 103 and a pressurizing roller 104start to rotate at a circumferential speed that is the same as the speedat which the recording material 20 is fed. When the forward end of therecording material reaches the pair of rollers 103 and 104, therecording material is held between the pair of rollers 103 and 104 andis further conveyed. When the recording material is held between theserollers, the center distance between the pair of rollers increases by anamount corresponding to the thickness of the recording material. Thisincrease is detected by a thickness sensor 105.

Regarding the thickness of the recording material, it is not alwaysnecessary to detect it by a sensor. The user may input information onthe thickness of the recording material to the device. In accordancewith the thickness of the recording material, the fixing speed ischanged and the inter-sheet distance is changed.

As described above, due to the two items of data supplied to theprocessing device, i.e., the data on the recording material size and thedata on the recording material thickness, parameters regarding thescattered toner and fog toner on the feeding belt, such as CPM(copies/minutes) and inter-sheet distance, are clarified, and theabove-mentioned processing device can output an optimum value forcleaning capacity switching.

FOURTH EMBODIMENT

While the above embodiments have only been described with reference tothe case in which, in a sheet-type cleaning member such as a cleaningweb, the switching of cleaning capacity is effected by changing theoutput timing for taking up the cleaning web, it is also possible tovary the speed at which the cleaning web is taken up. Further, it isalso possible to use a fur brush instead of the sheet-type cleaningmember. As compared with the case in which the cleaning capacity ismaintained by constant rotation at high speed, the progress of wear ofthe fur brush is restrained to an utmost degree while performingcleaning satisfactorily by changing to an appropriate rotating speed,thus achieving an increase in the service life of the cleaning device.Further, the wear of the surface of the feeding belt due to the fur beltcan be reduced. Further, the cleaning member may be a cleaning rollerformed by winding a non-woven fabric around a roller, and the cleaningcapacity may be varied by varying the rotating speed thereof.

Further, as shown in FIGS. 4 and 5, in addition to the sheet-typecleaning member, either a plate-type or a brush-type cleaning member,for example, a cleaning blade 23 or a fur brush 23' may be provided, andthe above-described switching of cleaning capacity may be effectedthrough contact or separation of the blade or the brush with or from thefeeding belt, thereby cleaning the surface of the feeding belt in asatisfactory manner.

Further, it goes without saying that the same effect can be obtained byan appropriate combination of the above-described control operations andmembers to vary the cleaning capacity.

In the first through third embodiments, the output timing for thecleaning member is varied so as to vary the cleaning capacity. In somecases, a plurality of ranks of recording materials as shown in the firstand second embodiments are used between one output and the next outputof the cleaning member. Taking this into consideration, it is desirable,as shown in FIG. 4, to vary the rotating speed of the cleaning memberaccording to the inter-sheet distance and the size of the recordingmaterial. That is, it may be arranged such that, the larger theinter-sheet distance, or the smaller the size of the recording material,the higher the rotating speed of the cleaning member.

What is claimed is:
 1. An image forming apparatus comprising:an imagecarrying member for carrying an image; a recording material carryingmember for carrying a recording material; transfer means fortransferring the image from said image carrying member to the recordingmaterial carried by said recording material carrying member; cleaningmeans for cleaning said recording material carrying member, wherein saidcleaning means includes a cleaning member and an auxiliary cleaningmember, which are capable of contacting said recording material carryingmember during cleaning of said recording material carrying member; anddetermining means for determining the distance between a rear end ofrecording material and a forward end of a next recording material whenimages are formed successively on a plurality of recording materials;wherein, said auxiliary cleaning member is used selectively in order tovary a cleaning capacity of said cleaning means in accordance with thedistance determined by said determining means.
 2. An image formingapparatus according to claim 1, further comprising fixing means forfixing the image on the recording material, wherein a plurality offixing speeds of said fixing means is selectable, and said distancebeing different in accordance with the selected fixing speed.
 3. Animage forming apparatus according to claim 1 or 2, wherein saidapparatus allows, after the formation of an image on a first surface ofa recording material, the formation of an image on a second surface ofthe recording material, and wherein said distance differs in accordancewith whether image formation is effected on the first surface of therecording material or the second surface thereof.
 4. An image formingapparatus according to claim 1 or 2, wherein said distance differs inaccordance with whether the recording material is an ordinary paper oran OHP film.
 5. An image forming apparatus according to claim 1 or 2,wherein said distance differs in accordance with whether the recordingmaterial is an ordinary paper or a paper having a thickness larger thanthat of the ordinary paper.
 6. An image forming apparatus according toclaim 1, wherein the timing of movement of said cleaning member isvaried in order to vary the cleaning capacity.
 7. An image formingapparatus according to claim 1, wherein the moving speed of saidcleaning member is varied in order to vary the cleaning capacity.
 8. Animage forming apparatus according to claim 6 or 7, wherein said cleaningmember consists of a web.
 9. An image forming apparatus according toclaim 1, wherein said auxiliary cleaning member is in the form of aplate.
 10. An image forming apparatus according to claim 1, wherein thecleaning capacity of said cleaning means is larger as the length of therecording material in the direction perpendicular to a conveyingdirection of said recording material becomes smaller.
 11. An imageforming apparatus according to claim 1, wherein said auxiliary cleaningmember comprises a brush.
 12. An image forming apparatus comprising:animage carrying member for carrying an image; a recording materialcarrying member for carrying a recording material; transfer means fortransferring the image from said image carrying member to the recordingmaterial carried by said recording material carrying member; cleaningmeans for cleaning said recording material carrying member, wherein saidcleaning means comprises a cleaning member and an auxiliary cleaningmember, which are capable of contacting said recording material carryingmember during cleaning of said carrying member, and wherein, when imagesare formed successively on a plurality of recording materials, saidauxiliary cleaning member is used selectively in order to vary acleaning capacity of said cleaning means in accordance with a length ofa recording material in a direction perpendicular to a conveyingdirection of the recording material.
 13. An image forming apparatusaccording to claim 12, wherein wherein the timing of movement for saidcleaning member is varied in order to vary the cleaning capacity.
 14. Animage forming apparatus according to claim 12, wherein the moving speedof said cleaning member is varied in order to vary the cleaningcapacity.
 15. An image forming apparatus according to claim 13 or 14,wherein said cleaning member consists of a web.
 16. An image formingapparatus according to claim 12, wherein said auxiliary cleaning memberis in the form of a plate.
 17. An image forming apparatus according toclaim 12, wherein said auxiliary cleaning member comprises a brush.